Docs/admin-guide/cgroup-v2: fix memory.stat doc details

Docs/admin-guide/cgroup-v2: fix memory.stat doc details

Fix minor cgroup v2 memory.stat documentation issues.  Correct the
vmalloc per-node marker now that vmalloc uses the native NR_VMALLOC node
stat, and document zswap_incomp as a byte-valued memory amount instead
of as a page counter.

Fixes: c466412c73c3 ("mm: memcontrol: switch to native NR_VMALLOC vmstat counter")
Fixes: 5ad41a38c364 ("mm: zswap: add per-memcg stat for incompressible pages")
Signed-off-by: Doehyun Baek <doehyunbaek@gmail.com>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>